Due to rapid innovation in the electronic communication technology, the welcome and preference of a cellular-phone handset depend on its outward appearance, size, and computing functions thereof. As for a wireless communication apparatus (such as a mobile phone), high reliability in the transmitting and receiving-signals, the quality and functionality of the antenna assembly play a major role in the mobile phone. The customer generally takes great consideration of the functionality and quality of the antenna assembly, when deciding in purchase of a mobile phone. It is therefore the prime object of the phone manufactures to improve the functionality and quality of the antenna assembly in the mobile phone.
Referring to FIG. 1, a conventional mobile phone, includes a base board 10 (a top planar view) and an antenna assembly mounted on the base board 10. The base board 10 includes multiple layers. The antenna assembly includes an antenna unit 12 and a plurality of conductive through holes 14. The antenna unit 12 includes an antenna body 120, a connector seat 122, and a feeding line 124. The antenna body 120, for example being helical-shaped, is seated on the connector seat 122. The feeding line 124 is coupled to a signal-processing module (not shown) of the conventional mobile phone. A ground layer (not visible) is disposed on a lower surface of the base board 10 while a radiating layer (not visible) is disposed on the upper surface of the base board 10. The conductive through holes 14 are used for guiding the coupled current generated in the ground layer to flow into the radiating layer so as to permit transmitting and receiving the radio signals.
FIG. 2 illustrates the flow direction of the coupled current in the base board 10, wherein the coupled current flows from the ground layer into the radiating layer via the conductive through holes 14. The ground layer is a full complete sheet (i.e. no opening or slot is formed therethrough), the coupled current flowing thereinto encounters no electrical impedance, thereby distributing the coupled current flow uniformly over the entire area of the ground layer. Under this condition, concentration of the coupled current flow into a specific portion of the ground layer cannot be achieved, which, in turn, shorten the effective current flow thereof, thereby restricting the transmission and receiving frequency bandwidth of the antenna assembly used in the conventional mobile phone.